What it means
The control module detected an open or otherwise faulty electrical circuit for cylinder 7 injector B. The code identifies the circuit fault; it does not establish what injector B refers to on a particular engine.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine control module monitors the circuit used to actuate injector B on cylinder 7. It stores P21D5 when that circuit appears open or electrically faulty, potentially leaving cylinder 7 without its commanded fuel; “injector B” must be identified from the vehicle’s service information.
Common causes
Most likely first.
- Open or damaged wiring
- Loose or corroded injector connector
- Injector electrical fault
Symptoms
- Check-engine light on
- Rough running or misfire
- Reduced engine power
- Increased fuel consumption
How to diagnose it
- Read freeze-frame data and check for companion cylinder 7 misfire or injector faults before clearing anything.
- Use service information to locate cylinder 7 injector B, then inspect its connector and harness for breaks, rubbing, corrosion, or heat damage.
- With the ignition off, unplug and inspect the cylinder 7 injector B connector for loose, bent, or recessed terminals and reconnect it firmly.
- Check continuity through the cylinder 7 injector B wiring and compare circuit results with the manufacturer's specification.
- If the harness and terminals pass, measure the injector’s electrical condition using the manufacturer's procedure to determine whether injector B itself is faulty.
Common fixes
- Restore a secure connection at the cylinder 7 injector B connector and clean corroded contacts.
- Repair or replace damaged wiring in the cylinder 7 injector B circuit.
- Replace cylinder 7 injector B if it fails electrical testing.
Can I keep driving?
If the engine is smooth and the check-engine light is steady, keep any necessary trip short and gentle while arranging diagnosis. A misfire or flashing light calls for stopping as soon as safely possible, since continued driving can worsen engine and emissions-system problems.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.